Poor tissue perfusion has an adverse effect on the healing process of tissue. To increase the chances of determining whether successful healing of, for example, acute and chronic wounds will occur, clinicians must correctly assess blood flow and tissue perfusion in and around the wound site. Furthermore, the ability to predict the potential for healing and the timeline of healing is also important. Usually, visual assessment of the wound, measurement of a reduction in wound area, and/or the percentage of wounds healed within a defined period is used as a scoring system for establishing a wound treatment protocol.
Certain advanced practices have begun to use imaging technologies such as fluorescence imaging technologies for assessing blood flow and/or tissue perfusion and establishing a prognosis for wound healing. Fluorescence imaging technologies may, for example, employ the administration of a bolus of an imaging agent (such as, for example, indocyanine green which binds with blood proteins in a subject) that subsequently circulates throughout the subject's vasculature and emits a fluorescence signal when illuminated with the appropriate excitation light. Fluorescence imaging systems acquire images of the emitted imaging agent fluorescence as the imaging agent bolus traverses the subject's tissue in the field of view. The images are typically acquired as the bolus enters the tissue through arterial vessels, travels through the tissue's microvasculature, and exits the tissue through the venous vessels. When the images are displayed as video on a monitor, clinicians may observe this imaging agent transit in the vasculature represented as variations in fluorescence intensity with time. Based on their visual perception of the fluorescence intensity, clinicians may make a relative, qualitative determination regarding the blood flow and/or perfusion status of the tissue and its subsequent healing potential. However, a qualitative visual evaluation of such images is not always sufficient for a number of reasons, particularly in instances where the visual information is ambiguous. For instance, such visual evaluation is limited since many parameters, such as image brightness, image contrast and image noise, can be affected by factors other than the blood flow and/or perfusion properties of the tissue. Moreover, mere visual evaluation is subjective (e.g., visual evaluation may vary from clinician to clinician, one clinician's visual evaluation protocol may vary somewhat from patient to patient and/or from imaging session to imaging session) and does not support a standardized protocol for assessing blood flow and/or tissue perfusion, and/or for assessing healing of tissue (e.g., progress of healing, efficacy of clinical intervention, etc.). Finally, due to a clinician's lack of memory or inaccurate recollection of previous visual assessments, it can be challenging to reliably and consistently compare and track blood flow, perfusion, and/or healing status of a patient over time across multiple imaging sessions.
The assessment of perfusion dynamics and a prognosis of tissue healing is also important in other clinical applications aside from wound care, such as, for example, pre-surgical evaluation of patients undergoing plastic or reconstructive procedures (e.g., skin flap transfers). For instance, it is desirable for fluorescence imaging systems to possess the data processing capabilities which consider parameters that reflect relevant perfusion dynamics and facilitate providing a prognosis for tissue healing. Furthermore, it is desirable for fluorescence imaging systems to present image data to the clinician in a manner that provides such information in a convenient and easily understood fashion.
It is therefore desirable to provide a tool that can aid the clinician in providing an accurate and reliable prognosis of healing potential of a tissue, chronicity or both. This will assist, for example, in ensuring that a correct diagnosis of the tissue is given, and that appropriate care is provided in a timely manner, therefore improving healing time and patient quality of life, and alleviating economic burden on healthcare systems.